This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ISO1640-Q1: Signal didnt cross the chip

Part Number: ISO1640-Q1
Other Parts Discussed in Thread: ISO1640

Hi,

My I2C signal didnt cross the ISO1640.

I am sure that the power supply on the is right.

My Schematic are as follow:

The signal on the side1 is correct while the signal on the side2 keeps in high level.

Data in the scope are as follow:

Can you please check my schematic?What may cause this problem?

I have changed a new chip for the test, but the problem still exist.

I wonder if a cap on the I2C bus is a must?

Please let me know if u need further information, THANK YOU!

Best,

ZHUO

  • Hello ZHUO, 

    Thank you for your question. See my comments below. 

    • Would it be possible to get a better picture of the schematic where all the connections to the IC are shown? 
    • Are C100 and C101 placed close to the supply pins in the layout (less than 2mm)? It is essential that the 0.1uF capacitor is placed as close as possible to the supply pin for correct switching behavior.  
    • How many I2C devices are connected to side 1 and to side 2? Load capacitances higher than the values recommended in the datasheet can lead to communication errors. 
    • How is P5_TOP generated?
      • This sounds simple, but I would recommend probing each pin of the IC to verify that they are at the proper voltage when idle. Specifically, check Vcc1, Vcc2, GND1 and GND2. 

    Best,
    Andrew

  • Hi Andrew,

    Thanks for your reply.

    1)My full schematic is as follows:

    PS: The footprint of TPL0401 is not correct. I have fixed this problem on the board.

    I did both tests with and without the I2C load (TPL0401,  the only load for the ISO1640). Both signals didn't come across the ISO1640.

    2)As for the layout problem, I got two places using the circuit whose schematic are exactly the same.

    In the first circuit, the capacitor is placed between ISO1640 and TPL0401, causing a slight gap (less than 3mm) between the capacitor and the power supply pins.

    However, in the second one, the cap is very close to the Vcc pin. The signal didn't come cross in both circuit.
    Test Result of VCC1 and VCC2 in the first circuit are as follow:
    3)Vcc2 comes from a isolated power block which transforms a 12V power supply on side1 to a 24V output in the side 2.
    Then, the 24V output is connected to a LM7805 to output a 5V to the side2 of the ISO1640. 
    Schematic is as follow:

    4)My I2C input signal is as follow:

    I am really confuse about this issue. What may possibly cause the problem?

    Let me know if you need further information.Your help means a lot to me.

    Thank you.

    Best,

    ZHUO

  • Hi ZHUO, 

    Thanks for the added details. From the information provided, nothing stands out as a significant issue. 

    Perhaps it is an issue with the PCB. Would it be possible to see your PCB layout? I would also be a good idea to remove the IC and test it outside of the system. 

    Best,
    Andrew